1. Technical Field
The invention relates to pneumatic tires, and, in particular, to a tire/wheel assembly for use in high brake heat generated service, such as buses used for mass transit, wherein the constant braking generates excessive heat, which can cause destruction of the tire bead interface. More particularly, the invention relates to such a tire/wheel assembly which enables a radial tire to be utilized on a larger diameter rim without increasing the overall height of the tire to provide lower heat generation in the area of the tire bead.
2. Background Information
Heat generated by the brakes of transit buses in city service through radiation, convection and conduction, results in high temperatures adjacent the bead area. This heat affects the bead area and lower sidewall of the tire and may cause ultimate tire breakdown, especially in radial tires which use steel-reinforced body plies. It is desirable to use radial tires for such vehicles, since the metal cords used as the reinforcing material in the belt provide excellent wear characteristics and puncture resistance under service conditions. However, as indicated above, the closeness of the bead area to the vehicle brakes causes excess heat generation in the bead area, possibly causing tire breakdown.
This heat generation problem can be reduced by increasing the size of the vehicle wheel or rim, thereby moving the tire bead further away from the heat-generating brake area. However, increasing the size of the wheel or rim will increase the overall size and height of the tire/wheel assembly. Such increase is unacceptable for many vehicles, such as those used in mass transit, where the height of the vehicle step is regulated by federal law and must be maintained. Therefore, just increasing the size of the wheel to reduce this heat generation problem is unacceptable due to the overall height increase of the tire/wheel assembly.
U.S. Pat. No. 4,082,132 discloses a radial tire for use with mass transit vehicles, which recognizes this heat generation problem and attempts to solve the same by a unique tire construction, and, in particular, a unique tread.
U.S. Pat. No. 5,137,069 discloses a new tire construction which desires to maintain the same tread width for use in drag racing but changes the cross-sectional configuration of the tire and the size of the rim or wheel.
U.S. Pat. No. 3,515,196 discloses a tire/wheel assembly which increases the wheel diameter without increasing the total diameter of the wheel and tire combination by providing the distance between the axial outer surfaces of the heel portions of the bead not less than 90% of the transverse sectional width of the tire, and wherein the sectional height of the tire is not greater than 77.5% of the sectional width of the tire.
U.S. Pat. No. 4,836,260 discloses a new rim or wheel configuration which provides increased brake space for a pneumatic tire without affecting the tire or its mounting thereon.
U.S. Pat. No. 5,131,446 discloses a pneumatic radial tire for heavy loads, such as trucks and buses, which avoids or reduces structural failure between the carcass and bead by a particular belt/ply arrangement.
U.S. Pat. No. 5,353,856 discloses a pneumatic radial tire which increases the durability of the belt layer without causing a decrease in the other characteristics of the tire when used for heavy-duty use by providing a modified tread area.
Although these prior art tires and tire/wheel combinations may achieve their intended purpose, there still exists a need for an improved vehicle tire and tire/wheel combination which enables a radial tire to be used for high brake heat generated service, such as mass transit buses, which achieves the effect by moving the tire bead further from the brake area without increasing the overall diameter of the tire/wheel assembly.